The present invention relates to digital wireless communication utilizing time division multiplex access, and more particularly to a dedicated channel entry method suitable for use with a setting procedure for a dedicated channel assigned to a slot.
Disaster preventing administrative wireless systems are now prevailing as preferential communication networks during disasters. In such systems, particularly in local disaster preventing wireless systems for municipal governments, digitalization has progressed and these systems have been reinforced as a means for rapid and controlled command communications.
Conventional techniques will be described with reference to FIG. 1A which illustrates an embodiment of the present invention including the portion same as conventional techniques. FIG. 1A illustrates an example of the structure of a local disaster preventing wireless digital system for municipal governments, mainly applied to mobile communications.
This system has a base station zone to be used by a control station constituted of a control apparatus 101 (including a command console 1) and wireless devices of a base station 2, and by mobile stations 3 constituted of mobile wireless devices such as mobile wireless apparatus and vehicle mounted wireless apparatus. For example, for an urgent notice during disasters, a command regarding safety information issued from the command console 1 is transmitted to mobile stations 3.
Time division multiple access (TDMA) is one of the systems realizing multiple access in which a plurality of mobile stations 3 share the same frequency band. A plurality of divided times (slots) are assigned to communication channels (Sch) and control channels (Cch). For communications, communication information is loaded in the communication channel, and control information is loaded in the control channel.
In some cases, a channel is selected from communication channels constituted of a plurality of slots, and is used as a dedicated channel to be used dedicatedly. This dedicated channel is assigned dedicatedly to administrative authorities as a communication line aiming at a particular use, for example, for an urgent command during disasters.
Conventionally, an entry to a dedicated channel has been made manually as a preparatory process of receiving voices of an urgent command.
FIG. 6 is a status transition diagram illustrating a conventional communication setting method for a manual entry to dedicated channel communications. Description will be made on the outline of a communication procedure among a command console 1, a base station 2 and a mobile station 3.
The command console 1 loads a communication channel number (slot number) to be designated as a dedicated channel on a control channel (Cch), and transmits the number to mobile stations 3, as a dedicated channel communication notice (S61).
The mobile station side can therefore enter a state allowing an entry to the dedicated channel. However, a selection right of the dedicated channel allowing an entry depends on a manual operation at the mobile station. In the state that the dedicated channel whose communication partner is the command console 1 is not selected, downlink voices (S62) issued from the command console 1 cannot be received (heard).
When the mobile station 3 enters the state that the dedicated channel whose communication partner is the command console 1 is manually selected, i.e., “the state of an entry to the dedicated channel communication by manual operation”, “channel switching” is performed from a normal control channel to the dedicated communication channel (dedicated channel) to establish “entry completion” to the dedicated channel, and downlink voices (S63) issued from the command console 1 can be received (heard).
With this arrangement, however, knowing whether the dedicated channel is being set in an urgent case necessary for communications is fully entrusted to judgment by an operator (or user) of each mobile station. Therefore, some mobile stations stand by for reception of the dedicated channel, and other mobile stations do not stand by for reception of the dedicated channel. There arises therefore a problem of inferior rapidness of command communications and low control reliability, such as that mobile stations desired to be participated in dedicated channel communications cannot participate.
A method of switching between general speech and dedicated speech has been proposed in which a mobile station in a general speech state set to the communication channel of general speech individually calls another mobile station in a dedicated channel communication state to perform communications by general speech. For example, refer to JP-A-2007-67562.